Conventionally, as pipe joints made of resin of this kind, those having configurations shown in FIG. 7 to FIG. 9 are known. Among them, the pipe joint made of resin shown in FIG. 7 comprises: a cylindrical joint body 34 in which a receiving port 30 is formed in one end portion in the axial direction, a primary sealing portion 31 intersecting the axis C is formed in an inner area of the receiving port 30, a secondary sealing portion 32 intersecting the axis C is formed in an entrance area of the receiving port 30, and an external thread portion 33 is formed on the outer periphery of the receiving port 30; a sleeve-like inner ring 40 in which a fitting portion 35 having an outer diameter that allows the portion to be fitted into the receiving port 30 of the joint body 34 is formed in an inner end portion in the axial direction, a bulge portion 36 having a mountain-like section shape is formed in an outer end side in the axial direction, the diameter of a resin pipe member 37 is increased when the fitting portion 35 is pressingly inserted into one end portion of the pipe member 37 under a state where the fitting portion 35 is outwardly projected in the axial direction, an inner end sealing portion 38 that abuts against the primary sealing portion 31 of the joint body 34 is formed in an end portion of the fitting portion 35, and a sealing face 39 that abuts against the secondary sealing portion 32 of the receiving port 30 is formed in a place corresponding to the bulge portion 36; and a pressing ring 42 having an internal thread portion 41 which is to be screwed to the external thread portion 33 of the joint body 34. Under a state where an insertion portion 43 of the pipe member 37 into which the inner ring 40 is pressingly inserted to be integrated therewith is inserted into the receiving port 30 of the joint body 34, the internal thread portion 41 of the pressing ring 42 is screwed to the external thread portion 33 of the joint body 34 to screwingly advance the pressing ring 42 toward the joint body 34, whereby the inner ring 40 is pressed in the axial direction to cause the secondary sealing portion 32 and the sealing face 39 of the inner ring 40 to respectively abut against the primary sealing portion 31 and the secondary sealing portion 32 of the receiving port 30 of the joint body 34, so as to exert a sealing force.
The pipe joint made of resin shown in FIG. 8 is configured in the following manner. A tapered sealing portion 46 in which the diameter is gradually reduced toward the inner side in the axial direction is formed in an entrance area of a receiving port 45 of the joint body 44 into which a one-end insertion portion 37a of a resin pipe member 37 is to be inserted. An outer ring 48 in which a sealing portion 47 that is to abut against the sealing portion 46 is formed in an inner end is fitted onto the insertion portion 37a of the pipe member 37, whereby a bulge portion 49 which is locally projected toward the radially inner side is formed on the pipe member 37. A pressing ring 52 having an internal thread portion 51 which is to be screwed to an external thread portion 50 formed in the outer periphery of the joint body 44 is screwingly advanced toward the joint body 44, whereby the outer ring 48 is pressed in the axial direction to cause the sealing portions 46 and 47 to abut against each other in the axial direction, so as to exert a sealing force.
The pipe joint made of resin shown in FIG. 9 is configured in the following manner. A tapered sealing portion 55 in which the diameter is gradually reduced toward the inner side in the axial direction is formed in an entrance area of a receiving port 54 of a joint body 53 into which a one-end insertion portion 37a of a resin pipe member 37 is to be inserted. An inner ring 57 which has a peripheral wall 56 having a trapezoidal section shape is pressingly inserted into the inner side of the one-end insertion portion 37a of the pipe member 37, whereby a bulge portion 58 which is locally projected toward the radially outer side along the peripheral wall 56 of the inner ring 57 is formed on the pipe member 37. A pressing ring 60 having an internal thread portion 59 which is to be screwed to an external thread portion 61 formed in the outer periphery of the joint body 53 is screwingly advanced toward the joint body 53, whereby the bulge portion 58 of the pipe member 37 and the inner ring 57 are pressed toward the joint body 53 to cause an inclined face 58a on the pipe end side of the bulge portion 58 to be pressed against the tapered sealing portion 55 in the axial direction, so as to exert a sealing force.
All the pipe joints made of resin of the conventional art which have been described above are configured so that the pressing ring 42, 52, or 60 is screwingly advanced to perform fastening, so that the sealing portion is caused to abut in the axial direction to apply a compression force, whereby a seal surface pressure is generated to exert a sealing function. Therefore, the pipe joints have a problem in that the sealing function is impaired for a short time period by reduction of the seal surface pressure due to a temporal creep or stress relaxation of the pressing ring 42, 52, or 60, the resin pipe member 37, or the like, and hence fluid leak easily occurs. Furthermore, the pipe joints have a low resistance to an external force, and, in order to ensure a predetermined sealing function, the fastening force of the pressing ring 42, 52, or 60 must be controlled very strictly during a connection work by means of the dimension in the axial direction or the fastening torque. Therefore, a connection work requires high skill and experience.